I have three Millenium seats in my Lund and have noticed they were "attracting" wasps and hornets. There is a hollow aluminum tube supporting the forward section of the seat and which is under the thigh when you sit down. Into this tube I have seen red wasps and bald face hornets enter. Their particular nesting habits probably preclude them from building a nest in the tube......I hope! However yesterday I noticed one end of one tube was occluded with grass. In fact grass was all over the floor under the seat. What could it be? Hopefully it is this: grass-carrying wasp | Roads End Naturalist
However, I would feel a whole lot better with those holes closed.